You have a few different ideals here.
The bodybuilder ideal.
My co-worker says he doesnt care if he can only bench press 5lbs as long as he can balance a glass of water on his upper chest.
If this is your mentality and you juice then obviously you dont have the highest regard for anything about your body other than the way it looks. Now this is not the mentality of everyone who does leg extensions, but a decent chunk I would guess. And further, people who do not think this way, for the most part probably make up a good chunk of those who do not like to do leg extensions.
The athletic ideal. Man I want a body that works. I want to be able to do handsprings, have a high vertical, be able to dunk, all that stuff. And its not even the fact that leg extensions would necessarily hurt my ability to do these things but that as great and amazing as all of those above abilities are, leg extensions are the most watered down castrated version of physical activity I can think of. But leg curls? Thats a different story.